This invention relates generally to methods and apparatus for excavating and in particular to methods and apparatus for penetrating rock and fracturing it by side thrust tensile forces.
Prior art devices for rapid drilling of holes in the ground or fracturing rock formations, in most cases by a crushing action, have consisted essentially of low velocity projectiles using shaped explosive charges, or explosive filled shells that were driven into the ground by propelling them from a gun. Some prior art devices utilizes a large mass projectile propelled from a gun at hypervelocities of 1.5 Km/sec. (4922 ft/sec.) and above. These high mass -- high velocity devices are used primarily to crush the rock material rather than penetrate it.
Projectiles using shaped explosive charges or explosive filled shells propelled from a gun operated satisfactorily in relatively soft material such as sand, loam, clay and similar material, however, they have not proved satisfactory for excavation or penetration of rock, in particular, the igneous rocks such as granite, diarite and basalt, or the metamorphic rocks such as the gneisses, marble, slate and coal, or the hard sedimentary rocks such as limestone.
For excavation of such hard rock materials, high mass nonpenetrating, hypervelocity projectiles have been used, projectiles having velocities greater than 1.5 Km/sec. (4922 ft/sec.). To reach such high velocity for such high masses, guns of special design are required which can withstand extremely high breach pressures and require special safety precautions for their operation. Such devices fail to efficiently fracture rock by compressional impacts at lower velocities because of the great waste of kinetic energy in the process of compression, deformation and shock wave transmission.